The present invention relates to a three-dimensionally controlled liquid crystal matrix display and to the control process for the same.
The invention more particularly applies to the field of optoelectronics and especially to the control of liquid crystal matrix displays, e.g. used as converters of electrical information into optical information, for the real time processing of optical images and for analogue display purposes.
FIG. 1a shows a cross-bar liquid crystal matrix display according to the prior art and FIG. 1b is an exploded view thereof. FIG. 1a shows two facing insulating walls 1, 3, which are kept spaced by a sealing joint 2 arranged on the peripheries thereof and between which is introduced a liquid crystal layer 4.
Over the inner face of wall 1 is distributed a first group of m parallel electrode rows, designated L.sub.i, with i being an integer such that 1.ltoreq.i.ltoreq.m, constituted by continuous conductive strips, whilst on the inner face of the other wall 3 is distributed a second group of q parallel electrode columns, designated C.sub.j, with j being an integer such that 1.ltoreq.j.ltoreq.q, whilst also being formed by conductive strips, the m and q columns of electrodes crossing one another. These m electrode rows and q electrode columns carry electrical signals, respectively row signal and column signals suitable for the excitation of the liquid crystal. The signals are produced in per se known manner by a power supply 6.
FIG. 1b shows an exploded view of the display with a first group of m electrode rows, designated L.sub.i and a second group of q electrode columns, designated C.sub.j, which are respectively distributed over walls 1 and 3. As the q electrode columns and m electrode lines cross one another, a liquid crystal zone I.sub.ij is defined by the overlap region of row L.sub.1 and the column C.sub.j. Each zone I.sub.ij defines and elementary image point of the display means, so that the latter comprises mxq image points distributed in matrix-like manner.
In general terms, to the m rows and q columns of electrodes are applied alternating electric signals in phase or in phase opposition, the amplitude of the row signals slightly exceeding that of the column signals.
When the signal of row L.sub.i and the signal of column C.sub.j are in phase, the resulting signal is equal to the difference of the amplitudes in absolute value of the row signal and the column signal. The resulting signal is then below the threshold voltage V.sub.s of the liquid crystal, corresponding to the minimum voltage necessary for exciting the liquid crystal. In addition, in the overlap zone I.sub.ij, as the liquid crystal is not excited, a black point is displayed. Conversely when the signal of row L.sub.i and the signal of column C.sub.j are in phase opposition, the resulting signal has an amplitude equal to the sum of the amplitudes in absolute value of the row signal and the column signal. The resulting signal produces an electric field in the overlap zone I.sub.ij, which generally brings about a collective orientation of molecules in said zone and consequently a white display.
By utilizing the selective orientation of the molecules and the punctiform excitation of the liquid crystal, an image is made to appear on the complete cell.
According to another type of known matrix display (called active matrix display), a counter electrode is provided in one wall and the electrode walls and columns are provided on the other wall.
With the intersection of each row and each column is e.g. associated a switch, such as a thin film transistor connected to a point electrode and, which transmits to the corresponding zone I.sub.ij defined by the overlapping of the point electrode and the counter-electrode, the signal resulting form the row signal applied to row L.sub.i and the column signal applied to column C.sub.j. Thus, there are the same number of transistors as there are image points.
In the aforementioned matrix display, in order to display mxq points, use is consequently made of a large number of transistors mxq, as well as a large number of connections m+q, said connections corresponding to all the inputs of electrical signals on the m rows and the q columns of electrodes.